Furnace for sintering metallic filaments for electric incandescent lamps.



G. TRENZBN & E. HAAGN.

FURNACE FOR SINTERING METALLIC FILAMENTS FOR ELECTRIC INCANDESGENT LAMPS.

APPLICATION T LED MAY 5,1911.

UNITED STATES PATENT Fries,

CARL TRENZEN, OF KOELN-BRAUNSFELD, AND ERNST HAAGN, OF HANAU, GERMANY; SAID HAAGN ASSIGNOR TO THE FIRM OF W. C. HERAEUS GESELLSCHAFT MIT BESCHRANKTER HAFIUNG, OF HANAU, GERMANY.

FURNACE FOR SINTERING METALLIC FILAMENTS FOR ELECTRIC INCANDESCENT LAMPS.

Specification of Letters Patent.

Patented Jun c 4, 1912.

Original application filed January 21, 1911 v Serial No. 603,852. Divided and this application filed May 5,

To all whom it may concern.

I x l Be it known that we, CARL 'linaxzux, a

subject of the terman Emperor, and resident of Koeln-iiraunsfeld, in the Province of llhineland, Kingdom of Prussia, German Empire, and l lnxs'r lluex, a subject of the Emperor of Am ia-llungary, and resident of Hanan, in the Province of Hesse-Nassau,

Kingdom of Prussia, German Empire, have invented new and useful lmprovements lll Furnaces for Sintering iletallic Filaments for Electric Incandescent Lamps, of which the following is a full, clear, and exact specification.

This invention relates to an improved furnace for sintering filaments of tungsten or similar metal, which have previously undergone the usual dccarbonizingtreatment. This sintening process has for its object to eliminate the'last traces of carbon and to impart to the tilamei'its a more dense structure as well as a greater durability. Here tofore this sintering process has been performed by causing an electric current to pass through each filament in the presence of a reducing gas. It has been proposed to externally heat such filaments in an atmosphere of such reducing gas without however, passing" an electric current thcretln'ough, in order to allow a certain number of filaments to be treated sinmltaneously. Second class conductors have been proposed as a material suitable for the sintering furnaces. Furnaces of this kind, however, have been found objectionable for the reason that for heating such furnaces by means of an electric current very high voltages are necessary and that in consequence, when the filamentcomes into contact with the inner side of the furnace, which could not always be avoided,

the electric current will not pass through the furnace, as it should do, but through the filaments themselves, which was the very thing to be avoided. Moreover, furnaces consisting of second class conductors are liable to be destroyed by reason of the diminished resistance occurring at high temperatures and by reason of the consequent increase of the passing current. It has also been' proposed to employ a furnace of iridium, but it Was practically remarked that in such case care must be taken to pre Serial No. 625,334.

t vent the tilaments from coming into contact with the incandescent sides of the furnace and thereby being baked thereto under the fritting action. To this end it had been proposed to coat the furnaces with second class coinluetors or to introduce the filaments into the furnaces by means of special carriers eon'iposed of the said material. A coating of this kind, however, does not last and will crack off by reason of the di'tt'erence in the coetlicient of expansion of the iridiuln and coating material, and the employment of special carriers of such materials presents certain ditliculties, apart from the fact that it is not always possible to avoid contactwith the inner sides of the furnaces with any degree of certainty.

\Ye haye found that the objections connected with the use of iridium furnaces are only experienced in such cases where the iridium employed is, as has always been the case heretofore, associated with other metals of the platinum group, more especially ruthenium, rhodium and platinum. \Vhen impurities of this kind are present even to a very moderate extent the metal of which the furnace consists can form an alloy with tungsten, and this will after a very short furnace. On the other hand, when employing a really pure iridiuln for the construction of the furnace there will be no danger of the filaments adhering to the inner sides of the furnace by fritting.

The object of our invention is to obviate the difficulties and objections connected with the furnaces heretofore employed in sintering' metallic filaments of the kind above referred to, and to this end our invention consists in the sintering furnace hereinafter to be more fully described and shown in the drawing, which shows an example of a furnace adapted for carryingout the improved process.

The essential feature of our invention is a tube of pure iridium in which the filaments which have undergone the usual preliminary decarbonizing treatment are sintercd by external heat without an electric current being allowed to flow through the filaments. This external heat is produced by heating the iridium tube by any appropriate means, and

period of time result in destruction of the preferably by an electric current. In this way it is possible to practically realize the object already aimed at heretofore, but not so far success-fully attained, of simultaneonsly treating a multiple number of filament-s without an electric current passing therethrough.

In the drawing the furnace is shown in The furnace itself-embodies the following arts: 5 .is a tube of pure iridium open at its lower end and closed at the top. By

means" of contact members 6 and 7 of a suitable conductin'g material, preferablyplatinum, the said tube is connected with two plates 8 and 9 preferably of nickel. These' =contact members 6 and 7 are prefer- -ably.so constructed as to be capable of a certain spring action, to thereby permit free expansion of the iridium tube '5 under the action 'of heat without thereby interferiugwiththe supply of elastic current. The plates'8 and 9 are supported on threaded boltslO secured to the transverse part 3 of the frame 2. A tube 11 of refractory material, preferably magnesia, surrounds the iridium tube 5 Without, however, contacting therewith at any point. The magnesia tube is surrounded by a cooling jacket 12 preferably made of nickel and adapted to have a cooling medium, such as water, supplied thereto through a pipe 14 which is provided with a cock or valve 13. 15 is a pipe for the discharge of the water from the cooling jacket 12. The lower portionof the iridium tube 5 isalso surrounded bya cooling jacket 16 to which cooling water is admitted through a pipe 17. 1 The discharge of :the water may be effected by means of a suitable pipe provided on the rear side, but not visible in the drawing. Another coolin jacket 18 having a water supply pipe 19 an a discharge pipe 20 also surrounds the upperportion of the iridium tube 5.

The iridium tube 5 is provided at its up per end'with a pipe 21, preferably'made of platinum, adapted to have a suitable reducing gas, such as hydrogen orammonia, supplied thercthrough. Another pipe 22, preferably also formed of platinum, serves for conveying the said reducing gas into the space between the iridium tube 5, on the one hand, and the magnesia tube 11 or the cooling jacket 12, on the other hand, the said gas then escaping at the lower end of the cooling jacket. It isof importance to thus admit gas exteriorly in order to thereby prevent the rather thin and, delicate iridium tube from being destroyed under the action of inner ressure and in order to secure the pure con ition of the gas WhlCl'l -1s-passed 'thethreaded bolts 10 already referred to by means of threaded nuts 25. he nickel plates 8 and v9 are provided with binding screws 26 for connecting an electric circuit thereto, Similar binding screws .are also provided at those corners of the nickel plates which are not visible in the drawing. The nickel plates 8 and 9 as well as the contact members 6 and 7 of the iridium tube 5 must be insulated from other metallic parts by suitable layers 27 of insulating material, such as asbestos slate, for instance.

On a cross piece 28 of the standard 1 are mounted two guide rods 29, 30 between which a ,rack bar 31 is arranged to slide upward and downward the said guide rods engaging in suitable grooves provided on the opposite sides of the guide rods. Apinion 32 rigid on the-shaft 33 suitably jou rn aled in bearings 34 of the st'andard 1 engages with the teeth of the rack bar, and by rotatingthe said shaft and its pinion 32 by means of its hand wheel 35 the rack. bar may be caused to move upward or downward. The said rack bar carries a holder 36 which is formed at its upper end for suspending therefrom the metal filaments 37 to be treated. This top portion of the-carrier 36 at least should also consist of pure iridium. For

the sake of clearness of the drawing only a few filaments are shown as suspended from the holder, but in the practical use of the invention a greater number of filaments will be suspended therefrom.

The practical operation is as follows: An electric current suitable for imparting to the iridium tube 5 the proper'temperature say 14001600 C. is supplied to the iridium tube 5 by way of the binding screws 26, nickel plates 8, 9 and contact members 6, 7

and caused to pass through the iridium tube 5, such currents being admitted at'a number of points simultaneously through the binding screws 26, since currents upto 1500 amperes are required. The filaments, after havmg been reliminarily heated at a temperature'of about 1250 C. in the well known manner, are assembled on the holder 36, and by rotating the hand wheel 35 the said holder is'raised and thereby moved into theiridium tube 5 from'below so that the filaments suspended therefrom will enter the highly 'heated portion 'of the said tube. During the operation a current of a reducing gas, such as hydrogen or ammonia, is introduced through the pipes 21 and 22, the passage of gas being so regulated that the gas will become substantially consumed and no-generr' ation of injurious gases can take place at the lower end to any appreciable extent.

aoeaesa The filaments having been allowed to remain from below as hereinbefore described, but

in that case the top end of the iridium tube will have to be provided with an opening for introducing the filaments, and such opening will have to be provided with means for closing the same. In this case provision will also have to be made for su tably admitting the gas laterally.

What We claim is:

1. In a sintering furnace the combination of a tube of pure iridium, means for passing electric current through said tube for heating the latter, a surrounding body of refractory material out of contact With. said tube, cooling devices surrounding tube and refractory body, means for admitting gas to the interior of said tube and between the tube and the surrounding body and cool ing devices, and means for lntroducing filaments into said tube.

2. In a sintering furnace the combi of a tube of pure iri ium I expand and contract under the indue' temperature variations, means "for p electric current through said tube for heating the latter, a surrounding body of retractory material out of contact With said tube, cooling devices surrounding said tube and refractory body, means for admitting reducing gas to the interior of said tube and between the tube and the surrounding body and cooling devices, and means for introducing filaments into said tube.

3. In a sintering furnace the combination of a tube of pure iridium arranged to freely expand and contract under the influence of temperature variations, means for passing electric current through said tube for heating the latter, a surrounding body of refractory material out of contact with said tube, cooling devices surrounding said tube and refractory body, means for admitting re ducing gas to the interior of said tube and between the tube and the surrounding body and cooling devices, a suspension device of pure iridium for carrying the filaments, and means for introducing said suspension device and filaments into said tube.

In testimony, that We claim the foregoing as our invention, we have signed our names in presence of tWo subscribing Witnesses.

CARL TRENZEN.

ERNST HAAGN. JJitnesses to the signature of Carl Trenzen:

Kain, Gnunriurr,

HENRY Crmnrnrne.

Ji "itnesses to the signature of Ernst EMIL litinz,

FRIEDRICH Ennuns. 

